else
  jQuery.globalEval( elem.text || elem.textContent || elem.innerHTML || "" );

 if ( elem.parentNode )
  elem.parentNode.removeChild( elem );
}

如果是<script src="xxxx.js"></script>则用ajax同步去读，否则用globalEval
 // Evalulates a script in a global context
 globalEval: function( data ) {
  if ( data && /\S/.test(data) ) {
   // Inspired by code by Andrea Giammarchi
   // http://webreflection.blogspot.com/2007/08/global-scope-evaluation-and-dom.html
   var head = document.getElementsByTagName("head")[0] || document.documentElement,
    script = document.createElement("script");

   script.type = "text/javascript";
   if ( jQuery.support.scriptEval )
    script.appendChild( document.createTextNode( data ) );
   else
    script.text = data;

   // Use insertBefore instead of appendChild  to circumvent an IE6 bug.
   // This arises when a base node is used (#2709).
   head.insertBefore( script, head.firstChild );
   head.removeChild( script );
  }
 },

    text.onclick=EventBuilder(container);
    //在这里无论是上面这种写法还是直接写function(){}结果占用内存都一样
    //只有直接引用外部函数如text.onclick=EventBuilder才能释放button对象,减少内存
    document.body.appendChild(container);
    document.body.appendChild(text);
    //如果onmouseover中我没有用到container 当然可以用 text=null container=null来打破循环引用
    //经测试用null打不破循环
}

function EventBuilder(container)
{
    return function(e)
    {
        alert(container)//这里container可访问
        text=this;//用this访问自身
    }
}
for(var i =0;i<5000;i++)
myButton()
//conclusion
闭包使返回的内部函数持有私有变量，所以此私有变量持有的dom对象不能被回收。
（被回收的条件：1。 没有context 2。没有被引用 ）
不内部写function。把内部变量传递给外部函数闭包返回不能解决问题。
所以唯一的方法是直接引用外部函数，如text.onclick = outFunc;

jQuery has full CSS 1-2 support and partial CSS 3 support, along with some custom CSS-like functionality (and XPath), as part of it's expression.

For info on how CSS works feel free to read the various links:

• CSS 1
• CSS 2
• CSS 3

What follows is a list of supported CSS Selector expressions.

• * any element
• E an element of type E
• E:nth-child(n) an E element, the n-th child of its parent
• E:first-child an E element, first child of its parent
• E:last-child an E element, last child of its parent
• E:only-child an E element, only child of its parent
• E:empty an E element that has no children (including text nodes)
• E:enabled a user interface element E which is not disabled
• E:disabled a user interface element E which is disabled
• E:checked a user interface element E which is checked (for instance a radio-button or checkbox)
• E:selected a user interface element E which is selected (one or more option elements inside a select) - not in the CSS spec, but nonetheless supported by jQuery
• E.warning an E element whose class is "warning"
• E#myid an E element with ID equal to "myid". (Will only match, at most, one element.)
• E:not(s) an E element that does not match simple selector s
• E F an F element descendant of an E element
• E > F an F element child of an E element
• E + F an F element immediately preceded by an E element
• E ~ F an F element preceded by an E element
• E,F,G select all E elements, F elements, and G elements

Supported, but different

All attribute selectors are written like their XPath counter-parts (in that all attributes should begin with an @ symbol).

• E[@foo] an E element with a "foo" attribute
• E[@foo=bar] an E element whose "foo" attribute value is exactly equal to "bar"
• E[@foo^=bar] an E element whose "foo" attribute value begins exactly with the string "bar"
• E[@foo$=bar] an E element whose "foo" attribute value ends exactly with the string "bar"
• E[@foo*=bar] an E element whose "foo" attribute value contains the substring "bar"
• E[@foo=bar][@baz=bop] an E element whose "foo" attribute value is exactly equal to "bar" and whose "baz" attribute is exactly equal to "bop"

Not supported

jQuery only supports selectors that actually select DOM elements - everything else is ignored.

• E:link
• E:visited an E element being the source anchor of a hyperlink of which the target is not yet visited (:link) or already visited (:visited)
• E:active
• E:hover
• E:focus an E element during certain user actions
• E:target an E element being the target of the referring URI
• E::first-line the first formatted line of an E element
• E::first-letter the first formatted letter of an E element
• E::selection the portion of an E element that is currently selected/highlighted by the user
• E::before generated content before an E element
• E::after generated content after an E element

jQuery doesn't support the following selectors due to their lack of real-world usefulness:

• E:nth-last-child(n) an E element, the n-th child of its parent, counting from the last one
• E:nth-of-type(n) an E element, the n-th sibling of its type
• E:nth-last-of-type(n) an E element, the n-th sibling of its type, counting from the last one
• E:first-of-type an E element, first sibling of its type
• E:last-of-type an E element, last sibling of its type
• E:only-of-type an E element, only sibling of its type
• E:lang(fr) an element of type E in language "fr"
• E[foo~="test"] an E element whose "foo" attribute value is a list of space-separated values, one of which is exactly equal to "test"
• E[hreflang|="en"] an E element whose "hreflang" attribute has a hyphen-separated list of values beginning (from the left) with "en"

Context and Anchoring

In jQuery, unlike real CSS, a selector expression may have a context other than the entire document, for instance with the function $(expr, context). You can anchor a CSS-like expression to the context root by starting it with one of the selectors >, +, or ~.

XPath Selectors

One of the selector languages that jQuery supports, as a part of its expression language is XPath. jQuery supports basic XPath expressions, in addition to CSS 1-3. Here are some samples:

Location Paths

• Relative to the entire HTML document

 $("/html/body//p")
$("body//p")
$("p/../div")

• Relative to the context node this

 $("p/*", this)
$("/p//a", this)

Supported Axis Selectors

• Descendant Element has a descendant element

 $("//div//p")

• Child Element has a child element

 $("//div/p")

• Preceding Sibling Element has an element before it, on the same axes

 $("//div ~ form")

• Parent Selects the parent element of the element

 $("//div/../p")

Supported Predicates

• [@foo] Has an attribute of foo

 $("//input[@checked]")

• [@foo='test'] Attribute foo is equal to test

 $("//a[@ref='nofollow']")

• [Nodelist] Element contains a node list, for example:

 $("//div[p]")
$("//div[p/a]")

Supported Predicates, but differently

• [last()] or [position()=last()] becomes :last

 $("p:last")

• [0] or [position()=0] becomes :eq(0) or :first

 $("p:first")
$("p:eq(0)")

• [position() < 5] becomes :lt(5)

 $("p:lt(5)")

• [position() > 2] becomes :gt(2)

 $("p:gt(2)")

Custom Selectors

jQuery includes some expressions that aren't available in either CSS or XPath, but were found to be very handy, so were included.

The following expressions' syntax is based upon the various CSS selectors, of similar names.

Custom Selectors

• :even Selects every other (even) element from the matched element set.
• :odd Selects every other (odd) element from the matched element set.
• :eq(0) and :nth(0) Selects the Nth element from the matched element set
• :gt(N) Selects all matched elements whose index is greater than N.
• :lt(N) Selects all matched elements whose index is less than N.
• :first Equivalent to :eq(0)
• :last Selects the last matched element.
• :parent Selects all elements which have child elements (including text).
• :contains('test') Selects all elements which contain the specified text.
• :visible Selects all visible elements (this includes items that have a display of block or inline, a visibility of visible, and aren't form elements of type hidden)
• :hidden Selects all hidden elements (this includes items that have a display of none, or a visibility of hidden, or are form elements of type hidden)

Some examples:

 $("p:first").css("fontWeight","bold");
$("div:hidden").show();
$("/div:contains('test')", this).hide();

Form Selectors

There are a few selectors for form elements:

• :input Selects all form elements (input, select, textarea, button).
• :text Selects all text fields (type="text").
• :password Selects all password fields (type="password").
• :radio Selects all radio fields (type="radio").
• :checkbox Selects all checkbox fields (type="checkbox").
• :submit Selects all submit buttons (type="submit").
• :image Selects all form images (type="image").
• :reset Selects all reset buttons (type="reset").
• :button Selects all other buttons (type="button").
• :file Selects all <input type="file">.

Also available is :hidden, see the description above for details.

It is recommended to provide a context when using the above:

 $('#myForm :input')

Or, if you have already a reference to your form:

 $('input:radio', myForm)

This would select all input elements of type radio inside myForm. Using :radio is mostly the same as [@type=radio], but should be slightly faster. Good to know when working with large forms